The present invention relates to a power transmission mechanism for transmitting driving power between a shaft and a rotor connected to the shaft and also to its assembling process.
Conventionally, some refrigerant compressors in vehicle air conditioning system are equipped with a power transmission mechanism 100, as shown in FIG. 4, for transmitting driving power from a vehicle engine to a drive shaft (c.f. Page 4 and FIG. 1 in Unexamined Japanese Patent Publication No. 2003-28183). A rotor 102 is rotatably supported by an extension of a housing 101 of the refrigerant compressor through a bearing 103, and the driving power is transmitted to the rotor 102 from the vehicle engine (not shown). A hub 105 is fastened securely to the outer end portion of a drive shaft 104 of the refrigerant compressor. The hub 105 is connected to the rotor 102 so as to be rotatable therewith. Thus, the driving power transmitted to the rotor 102 from the vehicle engine is further transmitted to the drive shaft 104 through the hub 105.
As shown in FIG. 5, a screw mechanism is used for fastening the hub 105 to the drive shaft 104. Specifically, the drive shaft 104 is formed at the end portion thereof extending out of the refrigerant compressor with an externally threaded portion 106. A screw seat member 107 having a screw seat surface 107a is fixed on the drive shaft 104 adjacent to and on the inner side of the externally threaded portion 106. The hub 105 is formed at its axial center with an internally threaded portion 108. The hub 105 is screwed onto the drive shaft 104 through engagement of their threaded portions 108, 106, and the inner surface of the hub 105 is pressed against the screw seat surface 107a of the screw seat member 107. Thus, the hub 105 is fastened to the drive shaft 104.
The drive shaft 104 has a whirl-stopper 109 at the end thereof that is held by a chuck (not shown) of an assembling machine when assembling the drive shaft 104 and the hub 105 by screwing, or when rotating either on of the drive shaft 104 and the hub 105 relative to the other during assembling. The diameter of the whirl-stopper 109 is smaller than that of the externally threaded portion 106 so that the chuck can hold the whirl-stopper 109 stably even when the hub 105 is located over the whirl-stopper 109 during relative screwing movement of the drive shaft 104 and the hub 105. Thus, this difference in diameter provides a space for permitting the chuck to hold the swirl-stop portion 109.
In the above-described power transmission mechanism 100, however, the hub 105 is tightened to the drive shaft 104 with a tightening torque greater than the maximum torque in order to prevent the hub 105 from sliding relative to the drive shaft 104 even when the torque to be transmitted between the hub 105 and the drive shaft 104 is at the maximum value of driving torque during normal operation (or the greatest torque). Thus, a great load is applied to the drive shaft 104 in assembling the drive shaft 104 and the hub 105 by screwing, so that there is a fear that the whirl-stopper 109 with a small diameter is broken at its base.
A fluid machine, for example, the above refrigerant compressor, has a shaft seal device 110 in the housing 101 for sealing the drive shaft 104. The shaft seal device 110 performs the function of sealing the drive shaft 104 while slidably contacting with the outer peripheral surface of the drive shaft 104. Thus, for the purpose of improving the durability of the shaft seal device 110, the drive shaft 104 is formed in such a way that the diameter of the portion thereof which is in slide contact with the shaft seal device 110 is smaller than that of the inner portion of the drive shaft 104, so that peripheral speed and hence the sliding contact at the former portion of the drive shaft 104 is reduced.
Since the drive shaft 104 is installed through the shaft seal device 110 by inserting firstly the whirl-stopper 109 thereof into the shaft seal device 110 in assembling of the refrigerant compressor, the diameter of the externally threaded portion 106, which are formed on outer portion of the drive shaft 104 than the shaft seal device 110, needs to be smaller than that of the portion of the drive shaft 104 that is in slide contact with the shaft seal device 110. As mentioned earlier herein, the diameter of the whirl-stopper 109 is still smaller than the externally threaded portion 106 in order to provide a space for the chuck to hold the whirl-stopper 109 of the drive shaft 104. Therefore, it is still harder to ensure sufficient durability of the whirl-stopper 109 and the whirl-stopper 109 tends to be easily broken during the work of screwing the drive shaft 104 and the hub 105.
The present invention is directed to a power transmission mechanism that prevents damage to a shaft during assembling and also an assembling process for the power transmission mechanism.